The present invention relates generally to apparatus for suspending and rotating rotors and, more particularly, but not by way of limitation, to the suspension and rotation of the impellors of pumps that can be implanted in the human body for replacing or assisting the natural heart in the pumping of blood through the circulatory system.
It has long been a goal of experimenters to develop a pump which can serve as an artificial heart and a variety of types of pumps have been designed to either replace or assist the natural heart in its function of pumping blood through the human body. While these prior art pumps have met with some degree of success, a number of problems associated with them have remained unsolved so that a practical artificial heart has not previously been developed. For a pump to be usable as a replacement or as an assist for the human heart, the pump must meet certain practical requirements which have been discussed in U.S. patent application Ser. No. 245,007, the teachings of which are hereby specifically incorporated herein by reference.
On a general level, the requirements for a blood pump are that it must not cause substantial injury to the blood and it must not require a large back-up system for its operation. Injury to the blood would preclude use of the pump over extended periods of time that would be required, for example, if the pump were to be a replacement for the natural heart or an assist that is to be implanted for the life of the patient. The size of the back-up system is a requirement that relates to the quality of life; for a pump to be practical, it must not require that the recipient be forever tied to an immobile life support system.
The requirement that the pump not require a large back-up system places certain technical requirements on the construction of a practical blood pump. One such requirement is that the pump be operable electrically so that the power supply for the pump can be provided by rechargeable batteries. At present, the technology is available to implant batteries within the human body and to recharge these batteries periodically using an induction coil that can be placed against the body as has been noted in the aforementioned U.S. patent application Ser. No. 245,007. Similarly, it is presently possible to build highly efficient, electrically operated pumps in which the pumping action is achieved by the rotation of an impellor to cause a liquid to be driven through a chamber in which the impellor is located. The problem that has not been solved prior to the present invention is to provide such a pump which will not cause unacceptable injury to blood.
A pump can injure blood in several ways. If the impellor of the pump is supported by mechanical bearings in contact with the blood, relative movement between parts of the bearings can result in excessive mechanical working of the blood causing blood cells to rupture. Glands which might be used to seal these bearings cannot solve this problem. Since the impellor will be moving with respect to the gland, blood in the neighborhood of the gland-impellor interface will be subjected to high sheer stresses and friction which can cause the rupture of blood cells in much the same manner that rupturing of blood cells is occasioned in a bearing.
Another mechanical effect that can injure blood is the formation of regions within the pump in which the blood is stagnant or in which eddies without sufficient blood exchange, equivalent to stagnation, may occur. Stagnation tends to result in coagulation of the blood.
A third effect that can injure blood is excessive heating as the blood passes through the pump. If the pump is inefficient, so that a large part of the energy supplied to the pump appears as heat discharged into the blood, blood cells may be damaged through overheating or coagulation of the blood may occur. In this regard, it should be noted that albumen begins to denature at 42.degree. C. so that inefficiency of the pump resulting in overheating of the blood can be a serious problem.